Remove support for the DeferredLibrary annotation and remove tests of it

tests/compiler/dart2js/deferred_emit_type_checks_test.dart

Index: tests/compiler/dart2js/deferred_emit_type_checks_test.dart
diff --git a/tests/compiler/dart2js/deferred_emit_type_checks_test.dart b/tests/compiler/dart2js/deferred_emit_type_checks_test.dart
index ecf6ffbf561d94335a98c5366cc0dd9ae1e6290e..db88e6a77b9ffc8c873372662cfb72d4ee89f346 100644
--- a/tests/compiler/dart2js/deferred_emit_type_checks_test.dart
+++ b/tests/compiler/dart2js/deferred_emit_type_checks_test.dart
@@ -51,7 +51,7 @@ void main() {
                                    {});
   asyncTest(() => compiler.run(Uri.parse('memory:main.dart')).then((_) {
     String mainOutput = outputs['main.js'].mem[0];
-    String deferredOutput = outputs['out_deferred.part.js'].mem[0];
+    String deferredOutput = outputs['out_lib.part.js'].mem[0];
     RegExp re = new RegExp(r"\n  _ = .\.A;\n  _.\$isA = TRUE;");
     print(deferredOutput);
     Expect.isTrue(re.hasMatch(deferredOutput));
@@ -63,14 +63,10 @@ void main() {
 // it with a type argument, and testing for the type. The extra support should
 // go to the deferred hunk.
 const Map MEMORY_SOURCE_FILES = const {"main.dart": """
-import "dart:async";
-
-@def import 'lib.dart' as lib show f, A, instance;
-
-const def = const DeferredLibrary("deferred");
+import 'lib.dart' deferred as lib show f, A, instance;
 
 void main() {
-  def.load().then((_) {
+  lib.loadLibrary().then((_) {
     print(lib.f(lib.instance));
   });
 }